Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/49—Phosphorus-containing compounds
  • C08K5/5398—Phosphorus bound to sulfur
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C1/00—Tyres characterised by the chemical composition or the physical arrangement or mixture of the composition
  • B60C1/0016—Compositions of the tread
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/0008—Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
  • C08K5/0025—Crosslinking or vulcanising agents; including accelerators
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/36—Sulfur-, selenium-, or tellurium-containing compounds
  • C08K5/43—Compounds containing sulfur bound to nitrogen
  • C08K5/44—Sulfenamides
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L21/00—Compositions of unspecified rubbers

Definitions

• Rubber compounds for use in pneumatic tires conventionally utilize a sulfur-based curing system incorporating several curatives, such as elemental sulfur or sulfur donors, accelerators, stearic acid, and zinc oxide. Recently it has become desirable to reduce the amount of zinc in the tire rubber. It would therefore be desirable to have a rubber compound and pneumatic tire cured using a cure system with the potential for a reduced zinc content in the rubber composition.
• curatives such as elemental sulfur or sulfur donors, accelerators, stearic acid, and zinc oxide.
• the invention is directed to a rubber composition in accordance with claim 1, its use in a tire tread, and a pneumatic tire in accordance with claim 15.
• the present invention is directed to a pneumatic tire comprising a ground contacting tread, the tread comprising a rubber composition comprising at least one additional diene based rubber; silica; a sulfur donor; a sulfenamide accelerator; and a dithiophosphate of the formula wherein Q is divalent Zn or S, R 3 may be identical or different, and R 3 is hydrogen or a monovalent hydrocarbon group of 1 to 18 carbon atoms; wherein the zinc content of the rubber composition is less than 0.5 parts by weight, per 100 parts by weight of elastomer (phr) as Zn meta.
• a pneumatic tire comprising a ground contacting tread, the tread comprising a rubber composition comprising at least one diene based rubber; optionally silica; a sulfur donor; a sulfenamide accelerator; and a dithiophoshate of the formula wherein Q is divalent Zn or S, R 3 may be identical or different, and R 3 is hydrogen or a monovalent hydrocarbon group of 1 to 18 carbon atoms; and wherein the zinc content of the rubber composition is less than 0.5 parts by weight, per 100 parts by weight of elastomer (phr) as Zn metal.
• This rubber composition may, however, also be used in other tire components or other rubber articles.
• the rubber composition includes a dithiophosphate of the formula wherein Q is divalent Zn or S, and R 3 may be identical or different, and R 3 is hydrogen or a monovalent hydrocarbon group of 1 to 18 carbon atoms. R 3 may be straight chain, branched, substituted or non-substituted alkyl or cycloalkyl.
• Q is divalent zinc
• the dithiophophate is a zinc dithiophophate.
• the dithiophosphate is zinc dibutylphosphorodithioate or zinc dibutylphosphorodithioate.
• Q is sulfur
• the dithiophosphate is a dithiophosphoryl polysulfide.
• the rubber composition comprises from 1 to 10 phr of a dithiophosphate. In one embodiment, the rubber composition comprises from 2 to 5 phr of a dithiophosphate.
• Zinc is added to the rubber composition in the form of zinc oxide or other zinc salts, such a zinc 2-ethylhexanoate and the like.
• the zinc content of the rubber composition is relatively low, to promote improved abrasion resistance of the rubber composition.
• the rubber composition has a zinc content of less than 0.5 phr as zinc metal. In one embodiment, the rubber composition has a zinc content of less than 0.2 phr as zinc metal. In one embodiment, the rubber composition has a zinc content of less than 0.1 phr as zinc metal.
• the rubber composition includes rubbers or elastomers containing olefinic unsaturation.
• the phrases "rubber or elastomer containing olefinic unsaturation” or “diene based elastomer” are intended to include both natural rubber and its various raw and reclaim forms as well as various synthetic rubbers.
• the terms “rubber” and “elastomer” may be used interchangeably, unless otherwise prescribed.
• the terms “rubber composition,” “compounded rubber” and “rubber compound” are used interchangeably to refer to rubber which has been blended or mixed with various ingredients and materials.
• the rubber composition optionally includes at least one additional diene based rubber.
• Representative synthetic polymers are the homopolymerization products of butadiene and its homologues and derivatives, for example, methylbutadiene, dimethylbutadiene and pentadiene as well as copolymers such as those formed from butadiene or its homologues or derivatives with other unsaturated monomers.
• acetylenes for example, vinyl acetylene
• olefins for example, isobutylene, which copolymerizes with isoprene to form butyl rubber
• vinyl compounds for example, acrylic acid, acrylonitrile (which polymerize with butadiene to form NBR), methacrylic acid and styrene, the latter compound polymerizing with butadiene to form SBR, as well as vinyl esters and various unsaturated aldehydes, ketones and ethers, e.g., acrolein, methyl isopropenyl ketone and vinylethyl ether.
• synthetic rubbers include neoprene (polychloroprene), polybutadiene (including cis-1,4-polybutadiene), polyisoprene (including cis-1,4-polyisoprene), butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutyl rubber, styrene/isoprene/butadiene rubber, copolymers of 1,3-butadiene or isoprene with monomers such as styrene, acrylonitrile and methyl methacrylate, as well as ethylene/propylene terpolymers, also known as ethylene/propylene/diene monomer (EPDM), and in particular, ethylene/propylene/ dicyclopentadiene terpolymers.
• neoprene polychloroprene
• polybutadiene including cis-1,4-polybutadiene
• rubbers which may be used include alkoxy-silyl end functionalized solution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupled and tin-coupled star-branched polymers.
• SBR alkoxy-silyl end functionalized solution polymerized polymers
• PBR polybutadiene
• SIBR silicon-coupled and tin-coupled star-branched polymers.
• the preferred rubber or elastomers are natural rubber, synthetic polyisoprene, polybutadiene and SBR.
• the rubber is preferably of at least two of diene based rubbers.
• a combination of two or more rubbers is preferred such as cis 1,4-polyisoprene rubber (natural or synthetic, although natural is preferred), 3,4-polyisoprene rubber, styrene/isoprene/butadiene rubber, emulsion and solution polymerization derived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers and emulsion polymerization prepared butadiene/acrylonitrile copolymers.
• a synthetic or natural polyisoprene rubber may be used.
• cis 1,4-polybutadiene rubber may be used.
• BR cis 1,4-polybutadiene rubber
• Such BR can be prepared, for example, by organic solution polymerization of 1,3-butadiene.
• the BR may be conveniently characterized, for example, by having at least a 90 percent cis 1,4-content.
• cis 1,4-polybutadiene rubber may be used.
• BR cis 1,4-polybutadiene rubber
• Such BR can be prepared, for example, by organic solution polymerization of 1,3-butadiene.
• the BR may be conveniently characterized, for example, by having at least a 90 percent cis 1,4-content.
• cis 1,4-polybutadiene rubber is used.
• Suitable polybutadiene rubbers may be prepared, for example, by organic solution polymerization of 1,3-butadiene.
• the BR may be conveniently characterized, for example, by having at least a 90 percent cis 1,4-content and a glass transition temperature Tg in a range of from -95 to -105oC.
• Suitable polybutadiene rubbers are available commercially, such as Budene® 1207 from Goodyear.
• the rubber composition includes a styrene-butadiene rubber.
• Suitable styrene-butadiene rubber includes emulsion and/or solution polymerization derived styrene/butadiene rubbers.
• an emulsion polymerization derived styrene/butadiene might be used having a relatively conventional styrene content of 20 to 28 percent bound styrene or, for some applications, an E-SBR having a medium to relatively high bound styrene content, namely, a bound styrene content of 30 to 45 percent.
• E-SBR emulsion polymerization prepared E-SBR
• styrene and 1,3-butadiene are copolymerized as an aqueous emulsion.
• the bound styrene content can vary, for example, from 5 to 50 percent.
• the E-SBR may also contain acrylonitrile to form a terpolymer rubber, as E-SBAR, in amounts, for example, of 2 to 30 weight percent bound acrylonitrile in the terpolymer.
• Emulsion polymerization prepared styrene/butadiene/acrylonitrile copolymer rubbers containing 2 to 40 weight percent bound acrylonitrile in the copolymer are also contemplated as diene based rubbers for use in this invention.
• S-SBR solution polymerization prepared SBR
• S-SBR typically has a bound styrene content in a range of 5 to 50, preferably 9 to 36, percent.
• the S-SBR can be conveniently prepared, for example, by organo lithium catalyzation in the presence of an organic hydrocarbon solvent.
• an emulsion polymerization derived styrene/butadiene may be used having a relatively conventional styrene content of greater than 36 percent bound styrene.
• E-SBR emulsion polymerization derived styrene/butadiene
• emulsion polymerization prepared E-SBR it is meant that styrene and 1,3-butadiene are copolymerized as an aqueous emulsion. Such are well known to those skilled in such art.
• a solution polymerization prepared styrene-butadiene rubber having a bound styrene content of greater than 36 percent may be used.
• Suitable solution polymerized styrene-butadiene rubbers may be made, for example, by organo lithium catalysis in the presence of an organic hydrocarbon solvent.
• the polymerizations employed in making the rubbery polymers are typically initiated by adding an organolithium initiator to an organic polymerization medium that contains the monomers. Such polymerizations are typically carried out utilizing continuous polymerization techniques. In such continuous polymerizations, monomers and initiator are continuously added to the organic polymerization medium with the rubbery polymer synthesized being continuously withdrawn.
• Such continuous polymerizations are typically conducted in a multiple reactor system.
• Suitable polymerization methods are known in the art, for example as disclosed in US-B- 4,843,120 ; US-B-5,137,998 ; US-B-5,047,483 ; US-B-5,272,220 ; US-B-5,239,009 ; US-B-5,061,765 ; US-B-5,405,927 ; US-B-5,654,384 ; US-B-5,620,939 ; US-B-5,627,237 ; US-B-5,677,402 ; US-B-6,103,842 ; and US-B-6,559,240 .
• Suitable solution polymerized styrene-butadiene rubbers may be tin- or silicon-coupled.
• suitable SSBR may be at least partially silicon coupled.
• Suitable solution polymerized styrene-butadiene rubber may be functionalized with one or more functional groups, including methoxysilyl groups.
• a reference to glass transition temperature, or Tg, of an elastomer or elastomer composition represents the glass transition temperature(s) of the respective elastomer or elastomer composition in its uncured state or possibly a cured state in a case of an elastomer composition.
• a Tg can be suitably determined as a peak midpoint by a differential scanning calorimeter (DSC) at a temperature rate of increase of 10oC per minute.
• DSC differential scanning calorimeter
• the rubber composition may also include up to 70 phr of processing oil.
• Processing oil may be included in the rubber composition as extending oil typically used to extend elastomers. Processing oil may also be included in the rubber composition by addition of the oil directly during rubber compounding.
• the processing oil used may include both extending oil present in the elastomers, and process oil added during compounding.
• Suitable process oils include various oils as are known in the art, including aromatic, paraffinic, naphthenic, vegetable oils, and low PCA oils, such as MES, TDAE, SRAE and heavy naphthenic oils.
• Suitable low PCA oils include those having a polycyclic aromatic content of less than 3 percent by weight as determined by the IP346 method. Procedures for the IP346 method may be found in Standard Methods for Analysis & Testing of Petroleum and Related Products and British Standard 2000 Parts, 2003, 62nd edition, published by the Institute of Petroleum, United Kingdom .
• the rubber composition preferably includes silica.
• the rubber composition preferably includes from 50 to 150 phr of silica. In another embodiment, from 60 to 120 phr of silica are used.
• siliceous pigments which may be used in the rubber compound include conventional pyrogenic and precipitated siliceous pigments (silica). In one embodiment, precipitated silica is used.
• silicas such as, for example herein, silicas commercially available from PPG Industries under the Hi-Sil trademark with designations 210 and 243, silicas available from Rhodia, with, for example, designations of Z1165MP and Z165GR; and silicas available from Degussa AG with, for example, designations VN2 and VN3.
• Commonly employed carbon blacks can be used as a conventional filler preferably in an amount ranging from 10 to 150 phr. In another embodiment, from 20 to 80 phr of carbon black may be used.
• Representative examples of such carbon blacks include N110, N121, N134, N220, N231, N234, N242, N293, N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539, N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907, N908, N990 and N991.
• These carbon blacks have iodine absorptions ranging from 9 to 145 g/kg and DBP number ranging from 34 to 150 cm 3 /100 g.
• fillers may be used in the rubber composition including, but not limited to, particulate fillers including ultra high molecular weight polyethylene (UHMWPE), crosslinked particulate polymer gels including but not limited to those disclosed in US-B-6,242,534 ; US-B- 6,207,757 ; US-B- 6,133,364 ; US-B- 6,372,857 ; US-B-5,395,891 ; or US-B- 6,127,488 , and plasticized starch composite filler including that disclosed in US-B- 5,672,639 .
• UHMWPE ultra high molecular weight polyethylene
• crosslinked particulate polymer gels including but not limited to those disclosed in US-B-6,242,534 ; US-B- 6,207,757 ; US-B- 6,133,364 ; US-B- 6,372,857 ; US-B-5,395,891 ; or US-B- 6,127,488
• plasticized starch composite filler including that disclosed in
• the rubber composition may contain a conventional sulfur containing organosilicon compound.
• suitable sulfur containing organosilicon compounds are of the formula: Z-Alk-S n -Alk-Z I in which Z is selected from the group consisting of where R 1 is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl; R 2 is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbon atoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is an integer of 2 to 8.
• the sulfur containing organosilicon compounds are the 3,3'-bis(trimethoxy or triethoxy silylpropyl) polysulfides. In one embodiment, the sulfur containing organosilicon compounds are 3,3'-bis(triethoxysilylpropyl) disulfide and/or 3,3'-bis(triethoxysilylpropyl) tetrasulfide. Therefore, as to formula I, Z may be where R 2 is an alkoxy of 2 to 4 carbon atoms, alternatively 2 carbon atoms; alk is a divalent hydrocarbon of 2 to 4 carbon atoms, alternatively with 3 carbon atoms; and n is an integer of from 2 to 5, alternatively 2 or 4.
• suitable sulfur containing organosilicon compounds include compounds disclosed in US-B- 6,608,125 .
• suitable sulfur containing organosilicon compounds include those disclosed in US-A- 2003/0130535 .
• the sulfur containing organosilicon compound is Si-363 from Degussa.
• the amount of the sulfur containing organosilicon compound in a rubber composition will vary depending on the level of other additives that are used. Generally speaking, the amount of the compound will range from 0.5 to 20 phr. In one embodiment, the amount will range from 1 to 10 phr.
• the rubber composition would be compounded by methods generally known in the rubber compounding art, such as mixing the various sulfur-vulcanizable constituent rubbers with various commonly used additive materials such as, for example, sulfur donors, curing aids, such as activators and retarders and processing additives, such as oils, resins including tackifying resins and plasticizers, fillers, pigments, fatty acid, zinc oxide, waxes, antioxidants and antiozonants and peptizing agents.
• additives mentioned above are selected and commonly used in conventional amounts.
• sulfur donors include elemental sulfur (free sulfur), an amine disulfide, polymeric polysulfide and sulfur olefin adducts.
• the sulfur-vulcanizing agent is elemental sulfur.
• the sulfur-vulcanizing agent may be used in an amount ranging from 0.5 to 8 phr.
• Typical amounts of tackifier resins, if used, comprise 0.5 to 10 phr, usually 1 to 5 phr.
• processing aids comprise 1 to 50 phr.
• Typical amounts of antioxidants comprise 1 to 5 phr.
• antioxidants may be, for example, diphenyl-p-phenylenediamine and others, such as, for example, those disclosed in The Vanderbilt Rubber Handbook (1978), Pages 344 through 346 .
• Typical amounts of antiozonants comprise 1 to 5 phr.
• Typical amounts of fatty acids, if used, which can include stearic acid comprise 0.5 to 3 phr.
• Typical amounts of waxes comprise 1 to 5 phr. Often microcrystalline waxes are used.
• peptizers comprise 0.1 to 1 phr.
• Typical peptizers may be, for example, pentachlorothiophenol and dibenzamidodiphenyl disulfide.
• Accelerators are used to control the time and/or temperature required for vulcanization and to improve the properties of the vulcanizate.
• a single accelerator system may be used, i.e., primary accelerator.
• the primary accelerator(s) may be used in total amounts ranging from 0.5 to 4.
• combinations of a primary and a secondary accelerator might be used with the secondary accelerator being used in smaller amounts, such as from 0.05 to 3 phr, in order to activate and to improve the properties of the vulcanizate.
• delayed action accelerators may be used which are not affected by normal processing temperatures but produce a satisfactory cure at ordinary vulcanization temperatures.
• Vulcanization retarders might also be used.
• Suitable types of accelerators that may be used in the present invention are amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates and xanthates.
• the primary accelerator is a sulfenamide.
• the secondary accelerator may be a guanidine, dithiocarbamate or thiuram compound.
• Suitable guanidines include dipheynylguanidine and the like.
• Suitable thiurams include tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetrabenzylthiuram disulfide.
• the mixing of the rubber composition can be accomplished by methods known to those having skill in the rubber mixing art.
• the ingredients are typically mixed in at least two stages, namely, at least one non-productive stage followed by a productive mix stage.
• the final curatives including sulfur-vulcanizing agents are typically mixed in the final stage which is conventionally called the "productive" mix stage in which the mixing typically occurs at a temperature, or ultimate temperature, lower than the mix temperature(s) than the preceding non-productive mix stage(s).
• the rubber composition may be subjected to a thermomechanical mixing step.
• the thermomechanical mixing step generally comprises a mechanical working in a mixer or extruder for a period of time suitable in order to produce a rubber temperature between 140°C and 190°C.
• the appropriate duration of the thermomechanical working varies as a function of the operating conditions, and the volume and nature of the components.
• the thermomechanical working may be from 1 to 20 minutes.
• the rubber composition may be incorporated in a variety of rubber components of the tire.
• the rubber component may be a tread (including tread cap and tread base), sidewall, apex, chafer, sidewall insert, wirecoat or innerliner.
• the component is a tread.
• the pneumatic tire of the present invention may be a race tire, passenger tire, aircraft tire, agricultural, earthmover, off-the-road or truck tire.
• the tire is a passenger or truck tire.
• Vulcanization of the pneumatic tire of the present invention is generally carried at conventional temperatures ranging from 100°C to 200°C. Any of the usual vulcanization processes may be used such as heating in a press or mold, heating with superheated steam or hot air.
• the invention is further illustrated by the following example.

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• 2010
  • 2010-09-30 US US12/894,295 patent/US20120083559A1/en not_active Abandoned
• 2011
  • 2011-09-23 BR BRPI1106272-0A patent/BRPI1106272A2/pt not_active IP Right Cessation
  • 2011-09-26 EP EP11182800A patent/EP2436727A1/fr not_active Withdrawn
  • 2011-09-30 CN CN2011102929540A patent/CN102443204A/zh active Pending

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